Split V3Hashed to V3Hasher and V3DupFinder (#2967)

V3Hasher is responsible for computing AstNode hashes, while V3DupFinder
can be used to find duplicate trees based on hashes. Interface of
V3DupFinder simplified somewhat. No functional change intended at this
point, but hash computation might differ in minor details, this however
should have no perceivable effect on output/runtime.

Implements (#2964)

src/V3Table.cpp

@@ -342,7 +342,7 @@ private:
 
     AstVarScope* findDuplicateTable(AstVarScope* vsc1p) {
         // See if another table we've created is identical, if so use it for both.
-        // (A more 'modern' way would be to instead use V3Hashed::findDuplicate)
+        // (A more 'modern' way would be to instead use V3DupFinder::findDuplicate)
         AstVar* var1p = vsc1p->varp();
         for (AstVarScope* vsc2p : m_modTableVscs) {
             AstVar* var2p = vsc2p->varp();